In the field of ultrasound diagnostics, acoustic images of body tissue are obtained. In order to produce real-time images, beams of ultrasound energy from an ultrasound probe are transmitted into the body tissue of a patient and echoes received by the ultrasound probe are rapidly processed to provide an image format suitable for display. Desirably, the probe will produce an image over a wide field of view using a sector scan format. A sector scan image is produced by repeatedly transmitting and receiving ultrasound energy in radial directions from the probe. The ultrasound beam is directed by a mechanically moving transducer which is physically swept about a pivot axis through an arc to produce a sector scan.
The prior art is replete with examples of ultrasound transducer probe assemblies, such as those disclosed in U.S. Pat. No. 4,149,419 entitled "Ultrasound Transducer Probe" issued Apr. 17, 1979 to R. Connell et al; U.S. Pat. No. 3,955,561 entitled "Cardioscan Probe" issued May 17, 1976 to R. Eggleton; U.S. Pat. No. 4,421,118 entitled "Ultrasound Transducer" issued Dec. 20, 1983 to J. Dow et al; U.S. Pat. No. 4,479,388 entitled "Ultrasound Transducer and Rive System" issued on Oct. 30, 1984 to T. Matzuk; U.S. Pat. No. 4,399,703 entitled "Ultrasound Transducer and Integral Drive Circuit Therefor" issued on Aug. 23, 1983 to T. Matzuk; U.S. Pat. No. 4,092,867 entitled "Ultrasound Scanning Apparatus" issued on Jun. 5, 1978 to T. Matzuk; U.S. Pat. No. 4,246,792 entitled "Self-Contained Ultrasound Scanner" issued Jan. 27, 1981 to T. Matzuk; and U.S. Pat. No. 4,398,425 entitled "Ultrasound Scanning Transducer" issued on Aug. 16, 1983 to T. Matzuk.
Such ultrasound probes commonly utilized an ultrasound transducer disposed within the probe head and oriented so as to radiate ultrasound energy from the probe head through a window formed therein. The probe head, and typically a portion of the body or housing of the ultrasound probe as well, is filled with an ultrasound transmissive fluid, typically an oil.
One long-standing problem commonly associated with such contemporary ultrasound probes is the formation of air bubbles within the ultrasound transmissive fluid. Such air bubbles, when disposed between the ultrasound transducer and the window, interfere with the radiation of ultrasound energy from the transducer into the patient, thereby degrading the performance of the ultrasound probe.
It is similarly undesirable to allow air bubbles to remain proximate the motor of an ultrasound probe. Such motors typically rely upon conduction provided by the ultrasound transmissive fluid to provide heat dissipation therefore. As such, air bubbles proximate the motor interfere with heat dissipation and may consequently result in substantial damage to the motor. Air bubbles may also potentially vary the electrical or dynamic characteristics of the motor in an undesirable manner. As such, according to contemporary methodology, it is desirable to eliminate or remove bubbles from the probe.
Visible air bubbles typically form within ultrasound probes when smaller, often invisible, air bubbles unite to form larger air bubbles, and as components of the ultrasound probe out gas various vapors. Additionally, various gasses dissolved within the ultrasound transmissive fluid are believed to accumulate as well.
As used herein, the term air bubbles refers to any gaseous bubbles formed within the ultrasound probe. Such air bubbles do not necessarily contain the well known components of air, e.g., nitrogen, oxygen, carbon dioxide, etc. Rather, as those skilled in the art will appreciate, such air bubbles may contain oil vapors, solvent vapors, and a wide variety of other gaseous components.
According to contemporary practice, such air bubbles are typically removed by technicians, typically at a maintenance facility. The air bubbles are frequently removed by draining and replacing the ultrasound transmissive fluid. However, the air bubbles may be removed by merely adding fluid to the ultrasound probe (topping off).
Filling of the ultrasound probe with oil is preferably accomplished under vacuum so as to prevent the undesirable introduction of gasses which may form bubbles therein.
Some manufactures provide a vent/fill hole in the housing of the ultrasound probe to facilitate the use of a syringe to remove bubbles therefrom and to facilitate the addition of oil thereto.
It is generally not desirable to have bubbles removed by the user, typically either a medical doctor or an ultrasound technician. The removal of bubbles from an ultrasound probe inherently requires that additional ultrasound transmissive fluid be added to the ultrasound probe to compensate for the volume of air removed therefrom. When such fluid is added by untrained personnel, the ultrasound probe is frequently filled with an undesirable fluid, thereby degrading the performance thereof and/or damaging the ultrasound probe. Frequently, the wrong type of oil is used to fill or top off the ultrasound probe. It has even been known for inexperienced personnel to add water to ultrasound probes, resulting in corrosion to the interior components thereof.
All prior art efforts to date have been focused upon removing air bubbles from the ultrasound probe so as to eliminate the well-recognized problems associated therewith. As discussed above and well-recognized by those skilled in the art, the removal of air bubbles from ultrasound probes presents inherent problems itself.
Although the prior art has repeatedly attempted to solve the problem of air bubbles disposed within the ultrasound probe housing, such repeated attempts have heretofore been ineffective since continued outgassing, leakage, etc., constantly replenishes the air bubbles. Thus, any attempt to remove air bubbles from the ultrasound probe is only temporarily effective since such air bubbles inevitably reform.
Further, thermal expansion of the ultrasound transmissive fluid is typically compensated for in contemporary ultrasound probes via a bellows which facilitate changes in the fluid filled internal volume of the ultrasound probe in response to temperature changes of fluid. However, not only are such bellows expensive, but they are also subject to leakage. As such, it is desirable to provide a means for eliminating the requirement for such bellows-type fluid expansion compensation means.